UPGRADING REPAIRING PCs

20
Chapter 2—System Components and Configuration
3. Designed by Cyrix, produced for Cyrix by IBM. Chips might be marked as “Cyrix” or “IBM”;
pin-compatible with Pentium.
4. Designed by Cyrix, produced by Texas Instruments and others. Chips might be marked as
“Cyrix” or “Texas Instruments.” Despite names, 486SLC was similar to 386SX, and 486DLC
was similar to 386DX.
5. Used as an upgrade to 486SX/DX-based systems.
6. Different internally from AMD’s chip, but also used as an upgrade to 486SX/DX-based systems.
7. Pin-compatible with Intel Celeron.
8. Uses new Socket A technology.
9. Future CPU model; will be capable of running new 64-bit instructions as well as 32-bit
Windows instructions; previously code-named “Merced.”
10. Future CPU model; is designed to run 32-bit Windows instructions.
Differences Between PC/XT and AT
Systems
Systems that feature an 8-bit memory bus are called PC/XT systems
after the pioneering IBM PC and IBM PC/XT. As you can see in
Table 2.2, the differences between these systems and descendents of
the IBM AT (16-bit memory bus and above) are significant. All
modern systems fall into the AT category.
Table 2.2 Differences Between PC/XT and AT Systems
System Attributes
PC/XT Type 8-Bit 16-, 32-, 64-Bit AT Type
Supported processors All x86 or x88 286 or higher
Processor modes Real Real, Protected, Virtual Real 2
Software supported 16-bit only 16- or 32-bit 2
Bus slot width 8-bit 16-, 32- 1 , and 64-bit 4
Slot type ISA only ISA, EISA 1 , MCA, PC-Card,
Cardbus 3 , VL-Bus 3 , PCI 3 , AGP 4
Hardware interrupts 8 (6 usable) 16 (11 usable)
DMA channels 4 (3 usable) 8 (7 usable)
Maximum RAM 1MB 16MB/4GB1 or more
Floppy controller 250 Kbit/sec 250, 300, 500, and
speed 1,000 Kbit/sec
Standard boot drive 360KB or 720KB 1.2M, 1.44MB, and 2.88MB
Keyboard interface Unidirectional Bidirectional
CMOS memory/clock None standard MC146818-compatible
Serial-port UART 8250B 16450/16550A or better
1. Requires 386DX-based system or above
2. Requires 386SX-based system or above
3. Requires 486SX-based system or above
4. Requires Pentium-based system or above