(^344) PC Hardware: A Beginner’s Guide
The Cover
Speaking of mounting things to the chassis, there are many ways to attach the cover to the
chassis. Most systems use a few screws to attach the cover to the chassis, but there are
screw-less or tool-less systems where the case hangs on the chassis using keyholes or
slide-and-lock features. However the cover attaches to the chassis, how snugly and se-
curely it fits is very important.
The case’s cover is designed into the airflow dynamics of the case as well as its RFI (radio
frequency interference) and EMI (electromagnetic interference) engineering. If your PC is
FCC- (Federal Communications Commission) certified, then the case was designed as
part of the RF emissions control of the PC. One of the risks of having a cover that doesn’t
fit tightly and securely without gaps or loose parts is that it could emit RF signals and affect
otherdevicesnearit.Anotheristhattheloosepartsofthecovermayrattleinthebreezeof
the escaping airflow, which would be a nuisance of the first order.
There is a wide variety of ways in which the outer cover of the case mounts to the
chassis. The most common way is to attach the cover with screws that bind the cover
piecestothefront,sides,andrearofthechassis.Itisveryrarethatyouneedtocompletely
remove the cover from the chassis. Normally, only the side (tower) or to p(deskto p) is re-
moved to provide access to the inside of the case. The following sections discuss the vari-
ous types of covers and how they are attached and removed from the chassis.Legacy Desktops
Until recently, the deskto pPC has been the most common of the case designs. There are
deskto pmodels for nearly every form factor (discussed later in the cha pter), including
the earliest PCs, such as the PC XT and the PC AT systems; the more common PCs, such
as the Baby AT and ATX systems; and the newer LPX slimline systems. For the most part,
older systems have a U-shaped piece that incorporates the covers for the top and sides of
the PC. This piece is attached to the chassis with four or five screws to the rear panel and
is removed by sliding it all the way back or forward off the PC or by sliding it back a bit
and then lifting it straight up. The benefit of this cover design is its simplicity, but you
mustbecarefulwhenremovingorreplacingitthatyoudon’tsnagpoweranddatacables,
expansion cards, or disk drives and dislodge or damage them.Legacy Towers
There are many different types of tower cases, but the oldest of the tower designs is typically
a full-sized AT, Baby AT, or ATX case. On these cases, the cover is a U-shaped piece with
very long sides that fit down and over the frame of the tower’s case. This cover is attached to
the rear of the case with four to six screws. To remove this cover, the screws are removed and
the cover is lifted straight u pand off, or it slides back a bit and then is lifted u pand off.