Quote from SLAC - Accounting Review - Perpetual vs Periodic (http://www.accd.edu/sac/slac/ppointshows/acct/perpetual_periodic.htm)
"Periodic Inventory System:
Under the periodic inventory system, the company usually waits until the end of an accounting period to take a physical inventory; it does not maintain detailed records of physical inventory on hand during the period. The cost of goods sold is computed after a physical inventory is taken.
Perpetual Inventory System:
Under the perpetual inventory system, records are kept of the quantity and usually the cost of individual items of inventory throughout the year, as items are bought and sold. The cost of goods sold is recorded as goods are transferred to customers, and the inventory balance is kept current throughout the year, as items are bought and sold."
That should answer your first question.
Hopefully this answers your second one.
The cost of goods sold is: (adding all this together) (With the exception of the returns and discounts; I am not really sure if these are expense accounts or not someone correct me on this please.) [This is also changed a little bit for Perpetual systems because the cost of goods sold is recorded as goods are transferred to customers]
- Your beginning merchandise inventory up for sale to customers
- Purchases to restore and add to your merchandise inventory
- Shipping cost of the purchases
- Purchases you return do to defauts (get your money back)
- Purchases discounts (save some money on what you buy)
Subtract all of this with the ending merchandise inventory to find out how much it costed you to buy and put up for sale your merchandise and how much of it you sold (hence the name cost of goods sold)
The reason for this account is to find out how much profit you made from your sales after you bought all the materials to put your items up for sale.
(Formula)
Net Sales - Cost of Goods Sold = Gross Profit on Sales
I'm assuming you know this but I'll put it up here just in case. Sales are the merchandise you put up for sale at a higher price then it costed you so you can make a profit; then you have your Sales Returns and Allowances account for people who return some of the goods you sold them from defects or other reasons. Subtract your returns from your Sales and this gives you Net Sales.
*EDIT* Oh and I don't think that the COGS appears in the journals/ledgers, just the separate accounts that make up the COGS appear on there. COGS only shows up in the Income Statement I believe. Someone correct me if I am wrong please.