addresses (see Chapter 13 for more information on system resources). The
display shows the resources assigned to each serial port by the BIOS.
Parallel ports The system resources assigned to parallel ports by the BIOS
is displayed.
Plug and Play devices If any Plug and Play (PnP) adapter cards are detected
by the BIOS, their information is displayed.ROMs, PROMs, and EPROMs: BIOS Chips
The BIOS programs and utilities are permanently stored on an electronic chip during
manufacturing. The program code is literally programmed into the chip, a process com-
monly described asburning in, when it is manufactured. The reasons for burning the
BIOS onto the chip are to prevent tampering or inadvertent changes to this vital program.
The BIOS must be able to run, or the PC is just a large paperweight sitting on a desk. The
following sections provide an overview of the electronic chips used to store the BIOS.Read-Only Memory (ROM)
As its name implies, data stored on aROM(Read-OnlyMemory)cannot be altered. Since the
chi pis read-only, it cannot be written to, which means it can only be read. Another benefit
of using ROM to store the BIOS is that it is nonvolatile.Nonvolatile memoryretains its con-
tents safely even after its power source is removed, which makes it an ideal media to store
system startu pinstructions. The most commonly used chi pfor BIOS programs is ROM. In
fact, BIOS is commonly referred to as ROM BIOS. Figure 6-4 shows a ROM BIOS chip.Programmable Read-Only Memory (PROM)
APROM(Programmable Read-Only Memory) is a kind of do-it-yourself ROM chi pready
to be programmed with data or programming. Using a ROM burner (a.k.a. ROM program-
mer), a PROM can be programmed with whatever data or programs you desire. The
PROM is programmed with the ROM burner by inducing a higher voltage (12 volts of di-
rect current [VDC]) than is normally used for PROM operations (5 VDC). The higher volt-
age burns a memory location and, where needed, turns a pre-existing binary 1 into a 0.
Once this process is done, it cannot be undone. The 0s cannot be made back into 1s. This is
whyPROMmemorychipsarealsoreferredtoasOTP(One-TimeProgrammable)memory.Erasable Programmable Read-Only Memory (EPROM)
A variation on the PROM chi pis theEPROM(pronounced “e-prom” and meaning
Erasable Programmable Read-Only Memory). The EPROM adds two important features
to the PROM; it is erasable and can be reprogrammed. EPROM chips can be reused and
don’t have to be discarded when its contents are obsolete. The one drawback is that to
reprogram the chip, it must be removed from the PC.(^118) PC Hardware: A Beginner’s Guide