User guide

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CLUSTER SIZE
Depending on the size of the partitions, there is always a 'minimum size' for a file to occupy,
known as a cluster under HDOS. A cluster is a group of sectors which is the smallest size
available for a file. This value varies depending on the 'disk' size. For instance, on a SS SD 100H disk,
the cluster size would be two sectors. On a very large partition, the cluster size may be more
than 20 sectors. This means, if you have a one sector file, although it will only occupy one physical
sector on the hard drive, the directory logs it off as twenty sectors for instance. If you do, for
instance, a CAT SY1:/ALL, you will see the actual disk sectors taken by each file. A CAT SY1:, for
instance, will show you the same files, but with their actual file size. When HDOS is assigned to over
50 cylinders for a partition, the CAT command may show an incomplete space remaining. This is
because only 4 digits were allocated when HDOS was designed and 5 digits are needed to show the
free sectors on a large partition. It's no big deal, but you should be aware of this. Once there are a
few files on the disk, the number will drop down below 9999, which will then accurately be
displayed. When checking the size on an empty partition, you may see something like 8734, which
is really 18734. Some examples of HDOS cluster sizes are listed:
CYLINDER SIZE
APPROX MEGABYTES
CLUSTER SIZE
100
5
76
75
3 ¾
58
50
2 ½
38
25
1 ¼
20
20
1
16
CP/M also has a limitation of a maximum number of directory entries which depends on the size of
the partition, and allows up to 8 megabytes per partition (not true for CP/M+). The HDOS
directory depends on the size selected, but at 1.2 Megabytes, the clus ter size is 20 sectors.
Listed below are cluster sizes and directory sizes for CP/M:
0 to 255K = 1K minimum per file
256K to 2 megabytes = 2K minimum per file
2 megabytes to 8 megabytes = 4K minimum per file
0 to 255K partition = 64 maximum directory entries