Information Technology Reference
In-Depth Information
take advantage of the special capabilities of disks and is not very ef
ficient. Instead, it is helpful to be able to split large files into several
pieces. File storage then requires two main tasks: locating where a
file begins and determining where subsequent pieces might be
found. To understand how these tasks are managed, we first need
to consider some basics of disk storage. Figure 3.2 shows a typical
organization of a basic disk.
As Figure 3.2 suggests, a disk is logically organized into a series
of concurrent rings, called
tracks
, and each track is logically subdi
vided into pieces, called
sectors
. (Different disks may have different
numbers of tracks or sectors, but the basic approach applies to any
disk storage.) File storage proceeds by allocating a series of sectors
for each file.
8 Sectors per Track Format with 40 Tracks
249
Sector
Sector
241
233
225
250
248
242
240
234
232
226
224
Sector
25
Sector
17
26
9
24
18
16
10
1
8
2
0
39
38
37
36
. . .
3
2
1
0
Track number
. . .
3
11 19 27
227
235 243 251
255 247 239 231
31 23 15
7
Sector number
4
6
12
5
14
22
20
28
13
21
29
30
Sector
Sector
228
230
236
244
238
246
254
252
229
237
245
253
Sector
Sector
Marker begins each sector
Sectors numbered 0 through 255
Tracks numbered 0 through 39
Figure 3.2
A typical disk organization.
