Selecting Hardware for a Linux System

In this article Phil Hughes describes the basics of choosing a hardware platform for Linux.

Although Linux software is virtually free, the required hardware isn't. This makes some people hesitate to jump into the Linux movement. But it doesn't need to be complicated, scary or expensive. Linux runs on most common hardware. In this article I will point out how to make the right choices and hopefully keep you away from costly mistakes. If you currently have a system that adequately runs MS-Windows, you probably have all you need for a decent Linux system. Although Linux is more sophisticated than MS-Windows, it doesn't require more hardware. In fact, because Linux is a pre-emptive multi-tasking system (this means that programs can be interrupted to service other requests), you can get a lot more useful work from the same computer. Before I get into specifics, I would like to point out that there is a lot of documentation on Linux. This includes HOWTOs which detail many of the specifics. These HOWTOs are available at Linux archive sites on the Internet, on most CD-ROM Linux distributions and on paper from various sources. A short article is no substitute for the details presented in the HOWTOs. I highly recommend that you get a copy and that you read them.

CPU and RAM

To run Linux you need a 386 or higher processor. For text-based applications even a slow 386SX system will perform very well. Although the Linux kernel is capable of emulating floating point arithmetic functions, it is significantly slower than a math co-processor; either in the form of a separate chip or a 486DX or better that has a built-in co-processor. The server system at the Linux Journal advertising/editorial offices is a 386DX40. It has proved to be a great performer with three high-speed modem lines connected to it, a local user and 2 or more active telnet sessions. It has 8MB of RAM but an upgrade to 16MB is planned. The system we use for running X-windows is a 486DX33 with 16MB of RAM. The built-in co-processor and additional RAM make this an excellent workstation for compute-intensive work. Linux needs a system that is based on the ISA (AT) or EISA bus. Linux does not support MicroChannel Architecture (MCA) machines such as the IBM PS/2. It does, however, support local bus systems such as VESA and PCI. What you need will depend on what you intend to do with the system. The minimum RAM is 4MB. If you currently have a 386SX with 4MB of RAM, give it a try. It may do all that you want with no investment. If, however, you need to purchase hardware to run Linux, look at higher performance systems such as something based on a 486DX chip and at least 8MB of RAM. The additional cost is not very great for a large performance increase.

Disks

There are two considerations: type and size. Linux supports MFM, RLL, ESDI and IDE disks with virtually any controller board. It also supports a fairly wide assortment of SCSI controllers. If you already have a system, you can probably stick with what you have. But, if you are purchasing new hardware, SCSI disks are well worth considering. Here's why: Many of the supported SCSI disk controllers use direct memory access (DMA) to transfer information. Under MS-DOS this has little advantage because MS-DOS (and MS-Windows) waits for input/output operations. On Linux, however, processing is overlapped with I/O. This means that a DMA controller can be transferring data while the CPU is processing other tasks. One of the most popular controllers supported by Linux is the Adaptec AH-1542C. It is relatively inexpensive ($200 range), uses DMA and has reasonable performance. For EISA bus systems, the AH-1742 may be used. If your system has a VESA local bus, the Buslogic 445S controller seems to offer the best performance at a reasonable cost. Other supported SCSI controllers include the Adaptec 152x series, Allways IN2000, Adaptec 1542 clones (including Buslogic 445S and 447S and DTC 3290 and 3292), Seagate ST01 and ST02, Western Digital 7000, Trantor T128 and T130B, Ultrastor 14F and 24F. The SCSI HOWTO has many details that will help you weigh the costs and performance of the various SCSI controllers. Another consideration when choosing between IDE and SCSI disks is that you can have two disks with IDE controllers and with SCSI you can have up to seven. Selecting the disk size requires some forethought about what applications you'll be running. The price of disk storage is dropping, and you can add one or more disks later on (depending upon your disk type). Linux can run on as small a partition as 20MB, but 200MB is a common size. Some applications may require disk sizes of 1GB or more.

CD-ROM

If you have a SCSI disk controller, a SCSI-based CD-ROM drive makes the most sense. It plugs into the same controller and works fine. With the advent of double and triple-speed CD-ROM drives, prices have dropped significantly on the single-speed drives which are adequate if all you intend to do is load files from a distribution CD-ROM. And prices for these devices on the surplus market seem to be in the $50-$80 range. If you are not using SCSI disks, using a non-SCSI CD-ROM is more cost-effective. Although others are supported, drives made by Mitsumi (and marketed under many names including BSR and Tandy) work well. They include their own controller card and can usually be found in the $150 price range.

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Phil Hughes

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