The Linux Hardware How To takes the approach that mainstream PC hardware is built for DOS and Windows. It focuses on the places where Linux has special requirements for its hardware. Well, we are now in an age where DOS is becoming less and less appropriate in that first sentence. Hence this section's title. Of course, special considerations with respect to the use of older hardware are also a focus here.
If you can reactivate an old PC, perhaps one lacking all the resources needed for running Windows, you may be pleased to find you have everything you need for a DOS based Internet workstation. I am thinking of PCs made between about 1984 and 1994. PCs older than that probably will lack sufficient disk or memory space for Internet software. Newer PCs, with suitable modems, also will be usable. However, the better they are at running Linux or Windows, the less you may appreciate running only DOS on them.
For the record, you'll need at least a fifteen or twenty MB disk and 640 KB of RAM to have much fun with DOS Internet software.
Your toughest call may come if your old PC is lacking a fast DOS compatible modem or a working disk or display. Remember that, working or not, an old system will have little or no market value. No matter what you've put into it. Don't consider the cost of replacement parts an investment.
If it doesn't make sense to repair your old PC, consider it a source of parts for reactivating the next old PC you find.
First of all, don't give up on an old disk without having made a serious
effort to reformat it. If your DOS has an FDISK or PART command, you may
need to use that ahead of FORMAT. You may as well if you only have one
partition or if all of the disk's partitions are blown.
Use: FDISK /STATUS
to see if there is anything left on your disk to be saved. You'll probably
need to Boot from a diskette in order to do this. Formatting can purge a
virus and make what looks like a "crashed" disk work like new! Of course,
all of your files will be gone.
Don't expect newer DOSs to be able to format a DOS v3.x machine's disk!
Again, use: FDISK /STATUS
to find out what your DOS and BIOS think of the disk you want to reformat.
With MS-DOS v5.0 and later, you'll need to use the FORMAT command's /U
switch to get it to completely ignore things it is still able to see on the
disk. (I always command: FORMAT x: /S/U/V
unless it complains about something in that.) Of course, formatting probably
won't restore a disk that actually has suffered a head crash.
The ATA IDE disk interface, that many inexpensive present day disk drives use, only became standardized after the 16 bit (two socket) ISA adapter bus had become popular. So popular that no one saw any point in trying to accommodate the 8 bit (one socket) ISA bus in the standard. The ATA IDE disk interface uses a single wide flat cable between the drive and the IDE "attachment". Another popular interface, the SCSI interface, tends to be used with somewhat more expensive disk drives. However, a used SCSI Host Adapter card may now offer the most affordable and practical way to give an old PC a modern replacement disk drive.
If you are considering buying a replacement disk, make sure your PC has an ATA IDE interface and BIOS support for it. It probably won't if it was made before about 1989. Other bad signs are an adapter bus with only 8 bit (single socket) slots. An 8086, 8088, or 80286 processor. An existing disk drive connected to its controller by two or more flat cables. The absence of a BIOS configuration arrangement. Or, information indicating that the system's original DOS was version 3.x. One practical way to repair the disk in those cases is to replace it, along with its controller, with a set from another similar vintage PC.
I am exploring the use of a parallel (printer) port connected Zip drive to augment or replace an old PC's disk. I have seen this working well with unpublished device driver software and DOS v3.3, on an 8088 based PC. The Zip drive is slower than my trusty (but, now dead) ST-225. However, I cannot recommend the published software I am presently aware of for this. (I e-mailed a bug report to its author on 13 July 2002.) If you want to experiment with this kind of arrangement, make sure you have all the data you value in your system backed up before you start! There is quite a bit more about these kinds of things in the ILNKFIX.TXT document offered in my ILNKFIX section. (Iomega's Zip drive software is said to require a '386 or later processor. Apparently, the parallel port Zip drive went out of new production in the middle of 2000.)
Lately, ATA IDE disk attachment interfaces have been coming in both parallel and serial versions. (Can you tell that everything above was written in an earlier era?) To sort these out, note that flat diskette drive cables have 34 wires. Parallel ATA (PATA) IDE disk attachments use 40 wire flat cables. (This is the traditional IDE attachment arrangement assumed above.) SCSI attachments use cables having 50 wires, or more. The newer Serial ATA (SATA) IDE disk attachments use cables having relatively few wires. Even fewer wires than diskette drive cables have.
If you do replace your disk with a giant new one, you'll need DOS v4 or later to be able to use more of it than just a few partitions no larger than about 32 MB, each. (Three of these 32 MB partitions fit neatly on a Zip 100 disk!) You'll still face an "8 GB Barrier" with MS-DOS versions 5, 6, and 7.0. You'll need MS-DOS v7.1 or v8, with FAT32 support, to be able to use more than 8 GB of your giant disk's space. All the MS-DOS versions with FAT32 support require a '386 or later processor. So, it seems safe to say that an '86/'88 or '286 based system will never be able to use more than 8 GB of a large disk's space.
Udo Kuhnt, http://www.drdosprojects.de/ , wrote to let me know that he is doing his best to disprove the preceding paragraph's final point. He has updated the DR-DOS v7.01 kernel and COMMAND.COM to enable their support of giant (i.e.: larger than 8 GB) disks, with FAT32 file systems. His DR-DOS v7.01.07 release works well on my oldest PC, Zeke, switched to either of its 8088 and '286 processors. We know that LBA BIOS ROM update cards were made for pre-LBA BIOS PCs, at one time. Some of the disk manufacturers have provided this kind of support in disk based software, too. So, in theory, DR-DOS v7.01.07 should be able to support a giant disk attached to a PC/XT! In addition to LBA BIOS software, a suitable set of supporting DOS command utilities would be required. And, probably, what would be a lot of RAM for an old machine. Both Udo and I are waiting to hear from anyone who succeeds in setting up a system of this kind.
If you do have a '386 or later processor: You still might choose to accept the 8 GB Barrier in your main DOS installation. But, dedicate the rest of your giant disk to Linux and Windows access. In that case, you'll need at least one EXT2 or EXT3 (for Linux only), FAT32 (for Linux and/or Windows), or NTFS (for Windows 200x or XP only) partition. (I haven't forgotten Windows NT. It uses an old version of NTFS that has been superseded by the new version of NTFS that Windows 200x and XP use.)
Partitioning gets real complicated when you try to have more than four partitions on a disk. So, with three 2 GB FAT16 partitions (make sure these go first on the disk) and an EXT2, EXT3, FAT32, or NTFS partition that is inaccessible from DOS, your DOS installation will then be limited to accessing no more than about 6 GB of disk space. Of course, Windows 98's "Real Mode" DOS will give you access to a FAT32 partition, too.
I don't recommend the Windows Millenium Edition's "Real Mode" or Emergency Boot Diskette DOS. Because that version has been stripped of things, like a working printer device driver, that can't be found in a Windows XP DOS window!
Today (in June 2009), there aren't many new ATA IDE disk drives available with a capacity of less than 160 GB! This means that you may run into a "32 GB Barrier", if your PC's vintage is from anywhere much before 2000. Or a "137 GB Barrier," with even newer PCs that don't have disk controller(s) which support the new 48-bit LBA standard.
The 32 GB Barrier is the result of your old PC's BIOS being unable to comprehend your giant new disk's size! Your BIOS might impose this barrier by hanging or stalling while sizing-up your machine at power-on or after a reset. If your new disk has a 32 GB strap, you might bypass this problem by using that. But, then you'll be losing all the rest of the space on your new disk. A better approach is to install the disk manufacturer's "Disk Manager" software. But, to do that, you've got to be able to Boot your PC with your new disk attached.
You can try to avoid that BIOS hang or stall by configuring the disk's
Cylinders, Heads, and Sectors (CHS) description, in the BIOS, to "safe"
values. CHS = 1023/16/63 may be as safe as anything. With a typical BIOS,
you enter something like:
User 1023 16 63 0 0 Normal
to provide that configuration. These settings tell the BIOS that the drive
has a size of only about 500 MB. If that will satisfy your BIOS and
eliminate its hang or stall, you'll be ready to Boot a Disk Manager software
diskette or CD ROM. The Disk Manager software will install a BIOS "overlay"
that helps it handle the disk's full size.
If you can't find a safe setting that will keep your BIOS from hanging or
stalling, you'll have to tell it to ignore your giant new disk.
With a typical BIOS, you enter something like:
None None
to provide that configuration. Unless there is confusion about something
like which drive is which, that is bound to satisfy your BIOS and eliminate
its hang or stall. So, you'll be able to Boot your PC. However, at that
point, there won't be any sign from the BIOS, of your new disk's presence.
Appropriate Disk Manager software or a Linux rescue system will be able to
see and manipulate your new disk without any help from the BIOS.
However, the Disk Manager won't be able to install its overlay software without at least one (other) Bootable disk drive present to put it on. Even a very small disk, like a 40 MB ATA IDE disk drive from a real old PC, will satisfy this need. But, remember that the life of the data on your giant new disk will depend on that small Boot disk, too. So, don't use a disk that appears to be in less than mint condition. Before you try to run the Disk Manager's installation software, make sure your small Boot disk is configured in the BIOS, partitioned, formatted, and Bootable. And, be sure the Disk Manager software can provide a diskette backup for its installation. So that you can replace the small Boot disk, if that should become necessary, without losing all the data on your giant disk.
Another kind of 32 GB Barrier may be seen in Windows 98's DOS. Its FORMAT utility usually refuses to work on a partition starting anywhere beyond a disk's 32 GB mark! Disk Manager or overlay software won't help with this barrier. However, an add-on 48-bit LBA controller will! As such an LBA controller also will provide a BIOS ROM, it seems likely to bypass both 32 GB Barriers without needing any help from Disk Manager or overlay software.
The 137 GB Barrier is the result of disk interface hardware that provides (only) 28-bit disk data addressing. The latest standard provides a 48-bit Logical Block Addressing (LBA) system. Intel is said to offer BIOS drivers that can bypass the 28-bit limit, for certain chipsets. Also, the disk manufacturer's Disk Manager software may provide a way to bypass the 28-bit limit, with Windows 2000 (SP3 or later) or Windows XP (SP1 or later). However, Disk Manager software won't be able to help DOS and Windows 9x with the 137 GB Barrier. It might not make sense to try to equip your old PC with an add-on 48-bit LBA controller. If so, it may be wise to simply plan on not having more than 137 GB, if that, of usable space on a giant new disk. That's still an amount that was just becoming imaginable in PCs about ten years ago!
Though FAT32 file systems may be set up on partitions larger than 32 GB, it may be wise to limit them to 32 GB. This is because Windows 98's file system maintenance tools: FDISK, FORMAT, and SCANDISK may start exhibiting bugs, of varying severity, when working with partitions larger than 32 GB. Four 32 GB partitions just fill a disk limited by the 137 GB Barrier. This makes another reason for not trying too hard to bypass the 137 GB Barrier, in an old system.
If you are considering buying a replacement display, check the connector on your PC's video card. If it doesn't have three rows of five pin holes each, you'll need a new SVGA video card for your PC, too.
Beware of used CRT displays priced at more than a very small fraction of their original cost. Assume that a used CRT display may die the day after your warranty expires. If no warranty, it probably will die tomorrow!
There are two basic varieties of dial line modems available for PCs. Then, as you'll see, there are different kinds of each of these.
Internal modems are built on a PC adapter card and plug into a slot inside your PC. With each passing year, the new models of these are becoming increasingly unlikely to be compatible with traditional DOS software. If they are compatible with DOS software, they'll contain electrical circuitry that provides the appearance of a traditional (or, "legacy") serial port to your software. More about this below.
External modems stand alone outside your PC and attach to your PC in one of two different ways. The kind that attach to a USB port won't be compatible with traditional DOS software. The kind that attach to a traditional (or, legacy) serial port are quite likely to be compatible with traditional DOS software.
Many of the internal modem cards available for PCs today are designed to fit a PCI slot. Obviously, you won't be able to use any of these if your old PC has only ISA slots. However, it isn't enough to get a modem card designed to fit one of your computer's slots, if you want to run DOS.
Today, many internal modem cards are designed to the Windows PNP and TAPI standards, even while designed to fit an ISA slot. (This is even more likely for modems designed to fit a PCI slot.) These standards are PC extensions that don't insure compatibility with traditional DOS software! I am not aware of any DOS Packet Driver emulating software for PPP that can work with an internal PNP modem or WinModem that doesn't come with DOS configuration software or a hardware settable non-PNP mode. I know of only one way to use a WinModem with DOS Internet software.
To get a new (read: fast) internal modem suitable for "Real Mode" (i.e., traditional) DOS software, you'll have to look for a "controller based" modem that comes in a box that proclaims DOS compatibility. If you have a real old PC with only 8 bit (single socket) ISA slots or a fairly new PC with only PCI slots, you'll have to be real careful.
First, I've noticed lately that even the internal modem boxes that mention DOS compatibility seem loath to disclose whether their contents require an 8 bit or 16 bit ISA slot! Of course, if the box proclaims support for IRQ(s) above 7, you know that a 16 bit slot will be required.
Second, if your PC has only 8 bit slots, the chances are that it is 8088 or 80286 based. Even if your new internal modem fits an 8 bit slot, it might have a configuration program that requires a '286 or '386 processor that you don't have. The beginning of my history.txt for DosLynx v0.20b discusses how hard it is to run such software on an 8088. This document may now be found in my DosLynx versions 0.2xb Documentation Package, which is offered at the end of this site's DosLynx Complete section. Your best bet is to seek a modem that has straps or switches that place it in a DOS compatible configuration that eliminates any need for a configuration program.
If you find the preceding paragraph frightening, another option is to use an external serial port connected modem. Not a USB port connected modem! The external serial port connected modem is bound to be compatible with your processor and DOS. If you have a suitable serial port to hook it to. And, the external modem probably will have indicator lights to help you see what is happening when you have trouble connecting. There are several downsides to this approach, however.
First, your serial port may present a serious bottle neck for your data. Try to see if you have a serial port with a 16550A type UART. (It is said that a 16550 without that A won't do. In the next section, I've reviewed some simple diagnostics you can use to find what kind of UARTs your serial ports have.) If you don't have a 16550A type UART, don't expect to be able to run that port at 56 K bits/sec. without losing data on an older (read: slower) PC. You might buy a new serial port card in order to get a 16550A UART. But, the cost of that on top of the cost of the external modem makes for a more expensive modem solution.
Second, with an external modem, you'll have another wall transformer to manage. And, a cable will be needed for connecting the modem to that serial port.
I used to mention a DOS compatible internal modem here. It was new in 2002. It had sold out of most stores by the end of 2004. There still may be one or two other(s) like it. But, now, you may find that you have little choice, in a new modem for DOS software, other than to go the external modem route.
See you on the 'net.
Fred C. Macall K8GIV
27 October 2021
